This is a Shannon Award providing partial support for the research projects that fall short of the assigned institute's funding range but are in the margin of excellence. The Shannon Award is intended to provide support to test the feasibility of the approach; develop further tests and refine research techniques; perform secondary analysis of available data sets; or conduct discrete projects that can demonstrate the PI's research capabilities or lend additional weight to an already meritorious application. The abstract below is taken from the original document submitted by the principal investigator. The research described in this proposal involves Electron Spin Resonance (EPR) and Electron Nuclear Double Resonance (ENDOR) studies of biologically important transition metal complexes. A new high field, high frequency instrument will be developed for these experiments. The 3-dimensional structure of metal binding sites will be determined from angle selected ENDOR experiments. The methodology for these types of experiments has been developed in our laboratory in recent years and one can now obtain single crystal like data from randomly oriented samples. Angles are selected by irradiation of the EPR transitions of molecules held at fixed angles with respect to an external magnetic field. The NMR spectra of these molecules are taken and NMR shifts are analyzed to yield dipolar and Fermi contact interactions. The dipolar interactions are used to determine the position of nuclei with respect to the metal ion. The geometry of ligand nuclei directly coordinated to a metal ion will be determined by ENDOR Induced EPR experiments. Structural studies of this type will be conducted with a series of model compounds, metal containing proteins, and hemoglobins. The high field EPR spectrometer should allow us to resolve small difference in g values which cannot be determined with lower field instruments. This g value information can be used to monitor the symmetry of the metal ion. The high field ENDOR experiments will have better resolution than those taken at low field and we expect to be able to obtain data which has previously been difficult or impossible to measure. ENDOR experiments will be conducted with protons, 14N, 31P, and 13C. ENDOR spectra of these nuclei which are difficult to resolve or detect with lower field instruments should be detected with high resolution with the high field ENDOR. This study will provide valuable new information on the structure of these complexes. Structural information of this type is necessary for an understanding of the mechanism by which these metal complexes function in a variety of biological processes.